Lately, among all types of rotary driving apparatus, the development of a dynamic pressure bearing apparatus that is essentially a rotor that rotates accurately at a high speed has advanced wherein a lubrication fluid generates a dynamic pressure to support a rotary shaft in the dynamic pressure bearing apparatus. For example, in the dynamic pressure bearing motor that is used for a hard disk drive illustrated in FIG. 5, rotary shaft 3 is rotatably inserted into bearing sleeve 2 having a hollow cylindrical shape and is attached to frame 1. A lubrication fluid is injected into a narrow gap between the dynamic pressure bearing sleeve 2 (hereinafter referred to as the “bearing sleeve”) and rotary shaft 3. A dynamic pressure bearing is thus constructed. The lubrication fluid generates a dynamic pressure to support rotary shaft 3 in a non-contacting manner. Rotary hub 4 is coupled in a manner that rotary hub 4 integrally rotates with rotary shaft 3.
Thin flat cover plate 5 is attached to the bottom end of the dynamic pressure bearing apparatus, which is opposite the surface end at which rotary hub 4 is joined together, as illustrated in FIG. 6, in such a manner that cover plate 5 closes the opening of bearing sleeve 2. The inner surface (upper end surface in the figure) of cover plate 5 in the inner portion toward the bearing is longitudinally arranged very close to shaft edge 3a of rotary shaft 3, which is the edge at the lower end of the figure. In the example illustrated in FIG. 6, a lubrication fluid is filled in the space partitioned by cover plate 5 in the inner portion toward the bearing such that it is continuous with the dynamic pressure bearing.
Herein, the edge toward the bottom end of frame 1 extends roughly parallel to the surface of cover plate 5 toward the outer end of the bearing and the product data label (product data plate) 6 (hereinafter referred to as “label”) on which desired data is visibly printed is adhesively attached to the edge of frame 1 toward the bottom end. Label 6 is printed with data such as date of manufacturing, lot number, and the manufacturer's name. Label 6 is attached to a place on frame A where the product data on label 6 is visible even when the dynamic pressure bearing motor M is attached onto the frame A in a hard disk drive apparatus, as illustrated in FIG. 7. More specifically, label 6 is attached to the area around cover plate 5 in such a manner that a circuit board or other components do not interrupt label 6. Label 6 of a conventional apparatus is adhesively attached to the bottom-end edge of frame 1 such that label 6 covers the entire outer surface of cover plate 5.
On the other hand, along with the recent trend of ever decreasing height of a rotary drive apparatus represented by a motor, the development of a thin dynamic pressure bearing apparatus, in which the longitudinal height of the bearing apparatus is reduced, has quickly advanced especially in the manufacturing of a hard disk drive apparatus. The preference for a thin dynamic pressure bearing apparatus induced the preference for a thin flat member for cover plate 5 and an extremely narrow gap between cover plate 5 and the longitudinal edge of rotary shaft 3. However, a thick label can be attached onto the cover plate much more efficiently than a thin label. As a result, insofar as a label is concerned, the situation is that the thicker the label, the better. This has provided an adverse effect on an attempt to reduce the longitudinal height of a dynamic pressure bearing apparatus.
In addition, where label 6 is adhesively attached in such a manner that it covers cover plate 5 as described above, one may unintentionally push cover plate 5 during attachment to deform cover plate 5. Once cover plate 5 deforms when a lubrication fluid is filled up to the inner end of cover plate 5, the lubrication fluid in the dynamic pressure bearing is pushed up in the shaft direction by the amount the cover plate 5 is deformed. This creates the possibility that the lubrication fluid may leak out from the open gap which is on the opposite end of bearing sleeve 2, subsequently deteriorating the bearing properties or lifetime of the dynamic pressure bearing.
Moreover, as is the case in the apparatus disclosed in Japanese patent application Laid-open (Kokai) No. 2001-289243, in an apparatus having a structure in which a lubrication fluid is filled in a space partitioned by the inner portion of the cover plate toward the bearing, the deformed portion of the cover plate may contact members toward the rotary shaft, causing abrasion or damage thereof. The contact by the deformed cover plate contaminates contacted members, further contaminating the lubrication fluid in the dynamic pressure bearing.
The apparatus in which a rigid plate constituting a thrust bearing is arranged to face the cover plate in the shaft direction is less likely to have the above problem. Nonetheless, the longitudinal height of the dynamic pressure bearing apparatus increases by the amount that the rigid plate occupies, which is an undesirable effect on the demand for a thin bearing.
Therefore, it is desirable to provide a very thin dynamic pressure bearing having excellent properties and lifetime even though a relatively thick label is attached thereto.